The Effect of Thickness on Optical Band Gap and N-type Conductivity of CuInS2 Thin Films Annealed in Air Atmosphere

Structural, electrical and optical properties of CuInS2 thin films of various thicknesses, grown on heated glass substrates at 100 °C by thermal evaporation method were studied. These films were annealed in air atmosphere at temperature of 200 °C. The thickness of the CIS films was varied from 436 to 80 nm. It was found that the structural properties, FWHM and grain size degraded with decreasing its thickness. The peak intensity decreases with the film thickness and the X-ray spectra are polycrystalline in nature excluding films with thickness less than 111 nm, the peak intensity disappears and films are amorphous in nature. However, with decreasing the film thickness from 436 to 111 nm, the optical band (Eg) gap of CuInS2 material is in the range 1.42 to 1.81 eV. Hot probe method showed that all the annealed CuInS2 samples exhibit n-type conductivity with low resistivity values in the range 3.60 to 0.08 kΩ.m. We suggests that the minimum thickness to obtain polycrystalline CuInS2 thin films is 111 nm, the band gap energy of CuInS2 thin films can be controlled by varying the film thickness and the n-type conductivity can be obtained after annealing in air atmosphere.